Aminophylline alters the core temperature response to acute hypoxemia in newborn and older guinea pigs

In newborns and adults of a number of species, exposure to acute hypoxemia produces a "regulated" decrease in core temperature, the mechanism of which is unknown. The present experiments were carried out on chronically instru mented newborn (5-10 days of age; n = 27) and older (25-30 days of age; n = 23) guinea pigs to test the hypothesis that adenosine mediates this regula ted decrease in core temperature. During an experiment, core temperature wa s measured by biotelemetry from animals studied in a thermocline during a c ontrol period of normoxemia, an experimental period of normoxemia or acute hypoxemia (fraction of inspired oxygen 0.10), and during a recovery period of normoxemia after an intraperitoneal injection of 10 mg/kg aminophylline (i.e., a nonspecific adenosine antagonist) or vehicle. Core temperature dec reased significantly during hypoxemia after vehicle in both newborn and old er guinea pigs. After aminophylline, however, newborn guinea pigs failed to significantly decrease their core temperature, whereas older guinea pigs e xhibited an attenuated yet significant core temperature decrease during hyp oxemia. Our data support the hypothesis that adenosine plays an age-depende nt role in mediating the regulated decrease in core temperature that occurs in newborn and older guinea pigs during acute hypoxemia.